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jm0278 avatar image
jm0278 asked

New Multiplus-II Briefly Ramps Charge Amps After Absorption Voltage First Reached

I've got a new Multiplus-II that I'm testing during the installation and I've now confirmed a troubling event that has occurred each time after the absorption voltage is first reached -- the charge current jumps from low single digits to at least the teens causing the voltage to jump up to over 14.6. This last test, the voltage got up to 14.7 on the Smartshunt despite the absorption voltage being set to 14.4.

The system is charging three 100Ah Battleborn batteries monitored with a SmartShunt. The current doesn't stay elevated more than about a minute, but during that time, it pushed the voltage perilously close to the batteries' built-in BMS high-voltage disconnect.

This behavior is not something I've observed in any other charging device including my other Mulitplus Compact and I'm concerned that at some point it's going to cause the BMS to disconnect.

Multiplus-IIbattery charging
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2 Answers
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snoobler answered ·

Reduce absorption voltage to 14.2V and see if the problem goes away. It may be triggering single cell high voltage disconnect due to a very slight imbalance.


The jump is likely the battery cutting off the charge circuit, and the 14.7V spike is the charger's reaction to losing its load instantaneously.

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jm0278 avatar image jm0278 commented ·
Good news and bad news. The good news is that reducing the absorption voltage to 14.2 kept the MP from exceeding Battleborn's recommended max of 14.6. The bad news is the ramp in current still happened and the battery voltage, all according to the Smart Shunt, got to 14.57 before tapering off again.

I watched the entire cycle very closely and the ramp actually appeared to happen in two stages. First, the current went from just over one amp while in Bulk mode to about 10 just after entering Absorption precisely at 14.2 volts. After remaining near 10 for some seconds, it definitely ramped a second time to 17. It was during this time that the voltage peaked at 14.57.

After peaking, the current dropped and the voltage gradually reduced to 14.19 at which point the current resumed what I now believe to be its normal method of absorption charging -- applying a small ~ one amp, current until the voltage is slightly above the absorption setting, then turning off the charger until the voltage drops to just below the absorption setting.

From my perspective, this is an acceptable situation but it does, to me, wreak of a software bug in the charging algorithm. Had I chosen to set the absorption voltage at the top of Battleborn's recommended range instead of the mid-point, it seems likely the battery's built-in BMS would have disconnected due to over-voltage.

Thanks for your help!

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snoobler avatar image snoobler jm0278 commented ·
I'm sorry, that doesn't sound normal at all. The proper behavior for a charger is to hold absorption and taper current never significantly exceeding the absorption voltage. That's how my Quattro behaves, how every 12V charger I've ever used behaves.


The only exception would be if the BMS cuts off charging, and the charger spikes the voltage before it can clamp down on the current - fraction of a second.


Are you sharing the smartshunt voltage data with the MP via a GX device?


You you using the VC voltage/current logging feature to capture what's going on?



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fkirsten avatar image
fkirsten answered ·

I have a similar problem with noresolution yet. See thread:


fkirsten asked · 1 day ago
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Multiplus 12 800 35 Overcharging Lithium batteries and then tripping

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